Sunday, July 03, 2016

Upper atmosphere cooling, CO2 and bluish sunsets

Global warming causes everything and is caused by everything. That seems to be the dogma of the Warmists. So we must not be surprised that global warming has been drafted in to explain noctilucent clouds, or more precisely, their greater incidence in recent decades. Their story is excerpted below.

The problem below lies with this statement: "While increasing carbon dioxide warms the surface of the Earth, those same molecules refrigerate the upper atmosphere". It is a conventional explanation of the well known fact that atmospheric layers above the tropopause are indeed getting colder.

So how so? What is the theory linking CO2 to upper atmosphere cooling? It relies on an assumption, that heat rising off the earth is blocked by tropospheric CO2 and hence is not available to warm the mesosphere and the stratosphere generally. The mesosphere is the lower part of the stratosphere.

So the big underlying assumption is to conceive CO2 as forming some sort of blanket around the earth. A blanket would indeed keep the heat in and deny it to the stratosphere. But CO2 is NOT a blanket. It is just lots of separate molecules jiggling away doing their own thing. And ANY heated atmospheric molecule will emanate its radiation in ALL directions -- not just downward towards earth. CO2 molecules don't have little compasses in them telling them in which direction to focus their radiations.

So CO2 is not a blanket at all. It will be just as likely to radiate upwards as downwards. It will be just as likely to warm the stratosphere as the troposphere. So once again Warmism is fundamentally flawed. CO2 does NOT explain stratospheric or mesospheric cooling.

One could argue that upward radiation is blocked by that peculiar layer called the tropopause but if we argue that way, what do we need CO2 for? Why do we need it to explain tropospheric warming? The tropopause already does the blocking job that CO2 is supposed to do. CO2 blocking becomes a surplus explanation that is put to death by Occam's razor. I don't think Warmists would want to go there.

So what, then, does explain the cooling of the stratosphere? I don't really think I need to go there. I don't have to have all the explanations. I will leave that pathology to the Warmists. I do however have some ideas centred around the fact that column ozone levels do differ in different parts of the world:

The stratosphere is where most of the earth's ozone is located. And incoming solar radiation breaks it up, producing warming. Where ozone levels are falling, there would be less warming and hence a cooling trend. And ozone levels DO appear to be falling, at least in Antarctica. The ozone hole there was at its largest late last year -- for all that the ozone hole warriors would have us think otherwise. I have dealt with their recent fantasy about that yesterday -- including their bizarre claim about how volcanoes work

So I can firmly say is that one part of the explanation for noctilucent clouds is faulty. The mesosphere is indeed getting cooler but global warming has nothing to do with it.

The second part of the explanation -- that methane promotes PMCs by adding moisture to the mesosphere, because rising methane oxidizes into water -- I have no quarrel with

In the summer of 1885, sky watchers around northern Europe noticed something strange. Sunsets weren’t the same any more. The red and orange colors they were used to seeing were still there—but those familiar colors were increasingly joined by rippling waves of luminous blue.

At first they chalked it up to Krakatoa, which had erupted just two years earlier. The explosion of the Indonesian super volcano hurled massive plumes of ash and dust into the atmosphere more than 50 miles high, coloring sunsets for years after the blast.

Eventually Krakatoa’s ash settled, yet the rippling waves of luminous blue didn’t go away. Indeed, more than 100 years later, they are shining brighter than ever.

Today we call them, "noctilucent clouds" (NLCs). They appear with regularity in summer months, shining against the starry sky at the edge of twilight. Back in the 19th century you had to go to Arctic latitudes to see them. In recent years, however, they have been sighted from backyards as far south as Colorado and Kansas.

Noctilucent clouds are such a mystery that in 2007 NASA launched a spacecraft to study them. The Aeronomy of Ice in the Mesosphere satellite (AIM) is equipped with sensors specifically designed to study the swarms of ice crystals that make up NLCs. Researchers call these swarms "polar mesospheric clouds" (PMCs).

A new study published in the Journal of Geophysical Research (doi:10.1002/2015JD024439) confirms what some researchers have long suspected: PMCs in the northern hemisphere have become more frequent and brighter in recent decades—a development that may be related to climate change.

At altitudes where PMCs form, temperatures decreased by 0.5 ±0.2K per decade. At the same time, water vapor increased by 0.07±0.03 ppmv (~1%) per decade.

"These results settle the decades old question of whether or not the observed long-term change in PMCs is an indicator of changing temperature or humidity," says James Russell, AIM Principal Investigator. "It’s both."

These results are consistent with a simple model linking PMCs to two greenhouse gases. First, carbon dioxide promotes PMCs by making the mesosphere colder. (While increasing carbon dioxide warms the surface of the Earth, those same molecules refrigerate the upper atmosphere – a yin-yang relationship long known to climate scientists.) Second, methane promotes PMCs by adding moisture to the mesosphere, because rising methane oxidizes into water.